function toRadians(d){
  return d*Math.PI/180
  }
  function getDistance(lat1,lng1,lat2,lng2){
    const R=6378137
    let dis=0
    let radLat1=toRadians(lat1)
    let radLat2=toRadians(lat2)
    let deltaLat=radLat1-radLat2
    let deltaLng=toRadians(lng1)-toRadians(lng2)
    dis=2*R* Math.asin(Math.sqrt(Math.pow(Math.sin(deltaLat/2),2)+Math.cos(radLat1)*Math.cos(radLat2)*Math.pow(Math.sin(deltaLng/2),2)))
    return dis  
  }
  module.exports={
    getDistance
  }